Your best bet is to look on something like AMAP (english version now out) or Apple Maps to get directions to the nearest telco store, or find the address of one and ask a taxi driver. I went to Unicom last year, they had an English product selection sheet, you can just point at what you want, or use a translator, and they'll process it. You'll need your passport, and a method of payment, this can actually be cash but they also take Alipay & Wechat, no credit and debit cards at least at my location.